Contextual Density and US Automotive CO2 Emissions across the Rural–Urban Continuum

Using data from the 2009 National Household Travel Survey, we quantify the effects of settlement patterns on individual driving habits and the resulting automotive carbon dioxide (CO 2 ) emissions. We employ CO 2 emissions to capture this impact accurately, as it reflects both vehicle miles traveled and any spatial differences in vehicle fuel efficiency choices. While previous studies have compared automotive travel in urban and suburban areas, our approach characterizes emissions across the entire US rural–urban gradient, focusing on the effects of population density. Rather than using categorical measures of contextual density (city, suburb, town, etc.), we use a geographical information system to calculate continuous measures of contextual density, that is, density at different proximities to households. These measures of contextual density allow us to model travel effects induced by the gravitational pull of the population densities of urban cores. Further, our methodological approach frames location choice as an endogenous treatment effect; that is, residential locations are not randomly assigned across our sample and significantly alter driving behavior. We find that individuals living in urban cores generate the lowest per capita automotive CO 2 emissions, due to close proximities of population concentrations. Rather than attracting individuals who would likely have low CO 2 emissions anyway, urban location apparently mitigates the emissions of people who would otherwise tend to have high automotive CO 2 emissions. We find larger elasticities with respect to density than previous studies and also find that the attractive forces of population densities affect driving patterns at distances up to sixty-one kilometers outside of urban areas.